Reinforced concrete road construction



April 8, 1969 P. o. K. WALZ ET AL 3,437,017

REINFORCED CONCRETE ROAD CONSTRUCTION Filed Aug. s, 1965 sheet of 3lat/L 0. A. WA LZ Andreas van SMM/3?. Max PASBERG A TTORIVEY April 8,1969 P.o, K. wALz ET AL 3,437,017

REINFORCED CONCRETE ROAD CONSTRUCTION Filed Aug. s, 1965 sheet 2 of 5Andreas von Sil/VMM Max Pasberg ay Wm A rmR/vey April 8, 1969 P. o. K.WALZ ET AL 3,437,017

REINFORCED CONCRETE ROAD CONSTRUCTION Filed Aug. s, 1965 sheet o of 5Max Pasberg nited States Patent Oice 3,437,917 Patented Apr. 8, 19693,437,017 REINFORCED CONCRETE ROAD CGNSTRUC'ION Paul Otto Kurt Walz,Dusseldorf, Andreas Van Schyndel,

Sturzelberg, Neuss, and Max Pasberg, Dusseldorf, Germany, assignors toBau-Stahlgewebe GmbH, Dusseldorf- Oberkassel, Germany, a corporation ofGermany Filed Aug. 3, 1965, Ser. No. 477,672 Claims priority,application Germany, Aug. 5, 1964, B 77,971; Nov. 21, 1964, B 79,426;Apr. 17, 1965, B 81,498; May 31, 1965, B 82,181

Int. CL E01c 1]/16 U.S. Cl. 94-8 6 Claims ABSTRACT F THE DISCLSURE In aconcrete roadway slab embodying a reinforcing steel mat composed ofspaced longitudinal rods extending in the lengthwise direction of theslab and spaced transverse rods intersecting and being aixed to saidlongitudinal rods, the transverse rods are bunched or subdivided intogroups with the rods Within each group having a predetermined spacingdistance and with the groups being spaced by intermediate regions freefrom transverse rods and having dimensions in the lengthwise directionof the slab substantially in excess of said rod spacing distance. Theintermediate regions serve as cushioning zones of the slab incooperation with socalled false equalizing gaps in the form oftransverse grooves provided in at least the upper surface of the slab ata position midway within said regions, said grooves defining fracturelines in the concrete. In order to afford ready equalization by the gapsformed at said lines during extreme temperature fluctuation cycles, thelongitudinal rod sections coincident with said intermediate regions arefitted with means, such as adhesion-resistant coatings, to provide forslidable engagement therebetween and the surrounding concrete, tothereby act 'as anchoring dowels for the concrete bodies on either sideof gaps formed upon initially subjecting the slab to a predeterminedlongitudinal stress in traffic.

The present invention relates to concrete road construction, moreparticularly to improvements in reinforced concrete road strips, slabsor plates provided with spaced gaps or weakened areas transverse of thelongitudinal direction of the slabs, more particularly of the type knownas false gaps in the art.

The incorporation of reinforcing inserts, such as steel mats or the likestructures, in concrete road slabs or plates has the purpose to preventor minimize the formation of cracks or fissures caused by longitudinaltensile stress or loads to which the slabs are subjected during use intrafiic. Ordinarily, or where only a relatively light load or traffic isexpected, the formation of cracks may be avoided or held Withinpermissible limits by the assurance of an efficient and uniformconnecting joint or adhesion between the concrete and the reinforcingstructures or members throughout the entire length of the slabs orplates. `On the other hand, in order to avoid the formation of irregularcracks or fissures in the slabs caused by tensile stresses resultingfrom relatively heavy loads or traffic, as well as due to extremetemperature fiuctuation cycles and other contractile excessive forces orstresses acting upon the plates, it has been found desirable tosubdivide each slab or plate into a multiplicity of sections by theprovision of transverse equalizing gaps of either the spacial or falsetype.

It has already become known, in place of providing so-called spacialgaps, or gaps completely initially separating the plates across theentire width or cross-section, to enable expansion and contraction byproper design manner as to produce false gaps, across said grooves,

to substantially prevent or minimize the formation of irregular cracksor lfissures in the plates or slabs under the effect of heavy loads ortrafiic.

`In the use of false gaps of this type, the normal reinforcements of theconcrete are omitted or completely interrupted at or in the vicinity ofthe gaps, in an effort not to impede or prevent the formation of thegaps by the presence or effect of the reinforcing members or inserts.The portions of the slabs or plates on the opposite sides of the gapsproviding a fracturing line, m'ay be connected by dowels or the likeconnecting members disposed advantageously in the central plane of theslabs, to resist vertical forces or loads on the plates, such additionaljoints or connections being substantially without effect on the mainconcrete reinforcement of the plates or slabs.

An important object of the present invention is the provision of areinforced concrete road slab of the referred to type, being constructedto positively prevent or minimize the formation of irregular cracks orfissures under relatively heavy load or trafiic conditions.

A more specific object of the invention is the provision, in connectionwith a reinforced concrete road slab of the referred to type having aplurality of false gaps formed therein in spaced relation andtransversely of the slab, of a reinforcing structure in the vicinity ofthe gaps designed to resiliently support or anchor the parts of theslabs on the opposite sides of the gaps, or to provide a cushioningeffect against longitudinal tensile stresses on the plates under heavyloads or traffic.

Another object of the invention is the provision of additionalreinforcing means adapted to withstand vertical loads on the plates,notwithstanding the resilient or cushioned mounting of the plates towithstand longitudinal stresses by the action of the false gaps and inthe manner as will become more apparent as the description proceeds.

The invention, both as to the foregoing and lancillary objects as wellas novel aspects, will be better understood from the following detaileddescription of a few preferred embodiments, taken in conjunction withthe accompanying drawings forming part of this specification andwherein:

FIG. 1 is a fractional longitudinal section of a reinforced concreteroad slab including a false gap and constructed in accordance with theprinciples of the invention;

FIG. 2 is a view similar to tion of FIG. 1;

FIG. 3 is a fractional longitudinal section of a reinforced concreteroad slab, being similar to the preceding figures and showing animproved feature of the invention;

FIG. 4 is a plan view of the reinforcing steel mat of FIG. 3, embodyingthe improvements of the invention;

FIG. 5 is similar to and showing a modification of FIG. 4;

FIG. 6 is an enlarged fractional view of FIG. 3;

FIG. 7 is a transverse section, taken along a false gap, of a reinforcedconcrete road slab or plate, showing yet another modification of theinvention;

and showing fa modifica- FIG. 8 is a plan view of the reinforcing mat ofFIG. 7, including the improvements of the invention;

FIGS. 9 and l0 are transverse sectional and plan views similar to FIGS.7 and 8, respectively, and showing still another modification of theinvention;

FIG. 1l is similar to and shows a modification of the embodimentaccording to FIG. 2; and

FIG. l2 is a perspective view of the reinforcing structure of FIG. ll.

Like reference characters denote like parts in the different views ofthe drawings.

With the foregoing objects in view, the invention, according to one ofits aspects, involves generally the provision, in a concrete road slabof the referred to type having a plurality of spaced transverse groovesor indentations in at least its upper surface adapted to create falsegaps thereat by fracturing of the concrete upon the slab being initiallysubjected to a predetermined longitudinal stress or load, of areinforcing steel mat structure embedded in and firmly adhering to theconcrete of the slab, said structure comprising essentially a pluralityof spaced longitudinal rods or bars extending in the lengthwisedirection of the slab and a plurality of spaced transverse rodsintersecting said longitudinal rods and connected thereto by welding orin any other suitable manner well known in the fabrication ofreinforcing steel mats or the like structures for use in concreteconstructions.

The transverse rods are omitted, in accordance with the improvement ofthe present invention, within predetermined intermediate cushioningzones or anchoring regions extending to preferably equal distances fromthe opposite sides of the gaps to be formed, whereby to providelongitudinal rod sections within said zones, only traversing therespective gap. In other words, the transverse rods are hunched orsubdivided into groups with the rods of each group having apredetermined spacing distance and with the groups being spaced byintermediate regions free from transverse rods and having dimensions inthe lengthwise direction of the slab substantially in excess of said rodspacing distance, to serve as equalizing or cushioning Zones for thegaps. Further means are provided to allow the longitudinal rod sectionswithin said zones to expand and contract freely as a result oflongitudinal forces or stresses normal to the gaps, under the conditionsof heavy loads or traffic and substantially unimpeded by the surroundingconcrete of the slab. In other words, the portions of the slab adjacentto the gaps are individually resiliently anchored by the interveninglongitudinal rod sections acting as dowels, whereby to substantiallyprevent irregular and other cracks or fissures in the plates or slabs,in a manner as will become further apparent as the description proceeds.

According to a simple embodiment to achieve the foregoing result andeffect, at least a fractional portion of the longitudinal rod sectionsWithin said cushioning zones is coated with an adhesion-resistantsubstance, such as a bituminous material, :a synthetic (plastic)material or the like, to allow the rods to move freely relative to thesurrounding concrete. Alternatively, the rod sections or parts thereofwithin the cushioning zones may be enveloped by sleeves or wrappings ofadhesion-resistant material.

The cushioning zones or regions in the vicinity of the false gaps mayeither be integral parts or sections of a composite reinforcing steelmat or equivalent structure for the enti-re concrete slab or strip, orseparate reinforcing structures for and in the vicinity of each gap andconstructed in accordance with the principles of the invention may beprovided.

In order to ensure adequate resistance against vertical forces orstresses on the slabs, that is, in the direction of the gaps, additionalreinforcing means may be provided in the cushioning zones, such as inthe form of longitudinal rods, tubes or bars, 'being supported either bythe longitudinal rod sections or by special supporting means providedtherefor, care to be taken to prevent the additional reinforcing membersfrom interfering with or impeding the free relative movement between thelongitudinal rod sections and the surrounding concrete. The foregoingaim may be achieved in a simple and eliicient manner by partially, thatis, within the region on one side of the gaps only, coating theadditional reinforcing members with Vadhesion-resistant material, toenable free relative movement of the concrete portions on the oppositesides of the gaps, or to provide an eicient resilient anchoring of theslabs, for the purpose and in a manner as will become further apparentfrom the following description in reference to the drawings.

Referring more particularly to FIG. 1 of the drawings, there is shown alongitudinal section of a fractional portion of a slab forming part of areinforced concrete l.road and including a false gap section constructedin accordance with the invention, it being understood that the entireslab or plate is provided with a series of spaced gaps or weakenedsections defining predetermined fracture lines, and associatedreinforcing structures, only one of which is shown and described in thefollowing.

More specifically, in the example shown by FIG. l, the slab section 1 isprovided upon its upper surface 2 with a groove or indentation 3extending transversely of and across the entire width of the slab, whilea T-shaped insert 4 of synthetic or the like material is embedded in theundersurface of the slab in line with the groove 2, in an effort tofurther reduce the cross-section of the slab to be fractured for theforming of the false gap or fracture 5 upon the slab being initiallysubjected in traffic to an adequate longitudinal tensile stress or load.The effect or function of the gap or fracture 5 is to prevent theformation of irregular cracks or fissures in the concrete surface byenabling a ready expansion and contraction within a cushioning oranchoring region a on the opposite sides of the gaps, under relativelyheavy load variations and temperature fluctuations to which the slab issubjected.

Mounted approximately in the central plane of the slab 1, FIG. l, is areinforcing steel mat or structure 6 comprised, in the example shown, oflongitudinal bars or rods 7 traversing the gap 5 and cross-rods 8 beingnormal to and secured to the rods 7 by Welding or in any other suitablemanner. The regularly spaced cross-rods 8 are omitted within thepredetermined cushioning zone or region a on the opposite sides of thegap 5 and the longitudinal rods 7, or the portions thereof within saidregion acting as dowels, are provided, either over the entire or afractional length of the zone a, with an insulating coating 9 or thelike adhesion-resistant covering adapted to prevent the formation of aclose joint or adhesion between the coated rod portions and thesurrounding concrete. The coating 9 may advantageously consist of abituminous or synthetic material. Alternatively, a covering sleeve maybe provided in lieu of coatings 9, as described in the folowing.

The omission of the transverse or cross-rods 8 within the zone a has theeffect of weakening the connecting joint between the mat 6 and thesurrounding concrete, while the adhesion-resistant coating 9 of the rodsacts to provide a kind of resilient anchoring for the longitudinal rods7 by virtue of the now possible expansion and contraction of the coatedrod sections. Besides, there is ensured thereby a safe fracturing of theconcrete at the desired cross-section or gap 5 for the purpose aspointed out hereinbefore.

It is understood that the mat 6 disposed in the center plane of the slabor plate 1 may be mounted in either the upper or lower third of theplate, to suit existing load or other operating conditions orrequirements. Besides, a number of mats may be embedded in a singleplate in spaced vertical relation and traversing the gap 5, in themanner shown. Furthermore, the mat 6 may be an integral part of a largerreinforcing mat or structure extending throughout the entire plate orslab 1, as indicated in FIG. 1, or individual unit mats or structuresmay be provided in the vicinity of each of the gaps 5, as shown in FIG.2. Finally, the mat structures of FIGS. l and 2 may be combined anddisposed in different vertical planes of a slab or plate 1, as will 4beunderstood. In order to support or properly position the mats within theslabs 1, suitable supporting or spacing devices may be provided inaccordance with conventional practice. Alternatively, the concrete maybe poured to a predetermined height or level and the mats positionedduring the pouring or laying operation.

The sections of the longitudinal rods 7 located within the zones a onthe opposite sides of the gaps 5 may serve to a certain extent to assumethe transverse load or forces on the plates acting in the direction ofsaid gaps. In order to resist additional transverse or vertical loads orforces, there are provided, in accordance with an improved feature ofthe invention, sleeves or tubular dowels concentrically enveloping therods 7 within the Zones a and connecting the separate slab portions Aand B on the opposite sides of the gap 5, in the manner more clearlyshown in FIG. 3 of the drawings. This not only substantially increasesthe capability of the mats to resist vertical loads or forces,notwithstanding the omission of the crossrods within the zones a, butfurther acts to ensure a safe or positive fracturing of the concrete andformation of the false gaps, since the thus obtained expansion path ofthe horizontal rods 7 within the tubes or sleeves 10 enables annnimpeded elastic expansion and contraction of the coated rod sections.

The reinforcing sleeves or tubular elements 10 should not affect theexpansibility of the plate or slab 1 for which purpose they are coatedupon at least the outer surface thereof with a layer of insulating oradhesionresistant material, as indicated by stippling in FIG. 4, orotherwise treated or conditioned so as not to impede the relativemovement of the rods 7. In many cases, it will be suicient to achievethis aim by coating the sleeves 10 over about one half of their lengthwith adhesionresistant material, as shown in FIG. 5, wherein the lengthc of the sleeves 11 is less than the length of the zones a, as comparedwith FIGS. 3 and 4, wherein the length b of the sleeves 10 equals thelength of the zones a. Advantageously, the coatings upon the sleeves 11should extend across the gaps 5 to a certain extent, as indicated inFIG. 5, to prevent corrosion in the region of the gap 5. In other words,in the latter case, the sleeves are coated and arranged to be inintimate connection with one of the plate sections A and B, while beingfree to move within the other section, in such a manner as to enablesaid sections to move freely if subjected to dimensional changes of theplates, such as expansion, contraction, creeping, etc. caused by load,temperature or other influences.

In order to further improve the free movement of the sleeves 10 and 11,a cap (not shown) or the like of metal, plastic, synthetic material,etc. may be mounted upon one end of the sleeves. The caps areadvantageously disposed alternately upon the opposite ends of thesleeves With enough free space ybeing left therebetween and the sleeves,to enable the latter and in turn the rod section 7 to move freely inrelation to the surrounding concrete.

The surface of the sleeves 10 and 11 is preferably circular, but may beelliptical or of any other desired shape. It is not necessary to providesleeves upon all of the rod sections 7 within the cushioning zones a,nor is it necessary for the sleeves to extend over the entire length ofthe zones, as in the case of the sleeves 10 of FIG. 4. FIG. 5 shows amat structure having auxiliary sleeves 11 of a length equal to afraction c of but greater than one half of the Width of the cushioningZone a. Finally, the sleeves 10 and 11 may be arranged upon the rods 7Cil in irregular fashion, but should be symmetrical to the gaps 5wherever possible.

Care should be taken to prevent liquid concrete to enter into the spacebetween the rods 7 and the sleeves 10 or 11 during theI concrete layingor pouring operation, especially where the inner space of the sleeves isnot completely occupied by the rods 7. If necessary, the ends of thesleeves may be closed yby means of seals 12 consisting of cork, putty,or a like sealing material, as shown in FIG. 6.

The constructions described in the foregoing make it possible to adaptthe reinforcing structures to any existing design and operatingconditions or requirements. The sleeves or dowels 10 and 11, if ofsuliiciently large diameter may have a reduced wall thickness comparedwith sleeves of smaller diameter, while the inner diameter may be suchas to snugly fit the rods 7, whereby to utilize the latter as additionalmeans to resist transverse or vertical forces, depending upon the' loadsor moment of resistance of the slabs in respect to the gaps 5.

There is thus provided, in accordance with the present invention, arelatively ilexible or resilient anchoring of the slab sections on theopposite sides of the false gaps of a concrete road slab or plate of thetype forming the subject of the invention, by the coated sections of therods 7 within the Zones a being enabled to expand under the effect ofheavy loads, to thereby avoid the formation of irregular cracks orfissures in t-he slabs or plates, as well as to eliminate other defectsinherent in the prior concrete road slab constructions. Additionally,the coated rod sections 7 may serve to resist transverse forces or loadseither separately or in conjunction with the additional reinforcingsleeves or dowels mounted upon the rods or carried by separatesupporting means, substantially without impairing the resilient supportor anchoring of the slabs, in the manner described and readilyunderstood from the foregoing.

The provision of resilient anchoring zones adjoining the false gaps inthe slabs or plates has the further advantage of preventing an unequalload distribution on the various gaps of a slab, whereby to in turnavoid concentrations of the total expansion upon a single gap or alimited number of gaps of a slab or plate.

Further embodiments of the invention to achieve the foregoing elfectsand results are Shown by FIGS. 7-10. FIGS. 7 and 9 are transversesections through a slab or plate, taken along a false gap 5, and FIGS. 8and l0 are plan views of the respective reinforcing mat structuresconstructed in accordance with the invention. Again, the longitudinalrods 7 of the mats disposed in the central plane of the slabs traversethe gap 5 and the cross-rods 8 are omitted within the Zones a on bothsides of the gaps, in substantially the same manner as in the precedingembodiments. Similarly to the latter, the rods 7 are covered bybituminous or the like coatings 9 within the zones a, in the manner andfor the purpose specied.

Two different types of additional reinforcements for the assumption oftransverse or vertical forces are shown in FIGS. 7, 8 and 9, 10,respectively. According to the FIG. 7 modification, sleeves or dowels 13of reduced length d are provided supported by semi-circular bents ordepressions 14 of a pair of auxiliary and transverse supporting rods 1Swhich are in turn supported, without being permanently aflixed thereto,by the longitudinal rods 7 engaging bents 16 in the rods 15 opposite tothe bents 14, in the manner shown by the drawing. If desirable, the rods15 may be positioned by loosely attaching them to the rods 7 by means oftwisted wire elements 17, or in any other suitable manner, to allow ofrelative sliding movements upon the rods 7.

FIGS. 9 and 10 show different types of profiled dowels 18 and 19 mounteddirectly upon the rods 7 within the zones a. More particularly, thedowels 18 of substantially circular cross-section are formed withlongitudinal grooves adapted to engage the coated sections lof the rods7, while the members 19 are of angular cross-section to t or overlie therods 7, in the manner shown and understood.

As is understood, the dowels 13 may have a suicient length, whereby tooverlie the first cross-rods 8 at the opposite ends of the zones a. Inthe latter case, the respective rods 8 may be formed wit-h bents,eyelets or the like, to receive or support the ends of the -dowels 13,in a manner similar to the auxiliary supporting rods 15. In either case,the auxiliary dowels or rods should be provided wth adhesion-resistantcoatings over at least one half the length thereof, to provide ayielding support or anchoring of the slab portions on the opposite sidesof the gaps 5, in accordance with the basic concept and principles ofthe invention.

As pointed out hereinbefore, the special reinforcing structures Withinthe zones a of the false gaps S according to the invention may be anintegral part of a composite steel mat or the like reinforcing structureextending over the entire concrete road slab or strip, as indicated inFIG. 1, or separate or discrete mat structures may be provided in thevicinity of each of the gaps, as shown in FIG. 2. Moreover, thereinforcing structures, in place of being in the form of planar mats orassemblies, may be of any, including a three-dimensional, type orconstruction with the cross-rods being omitted within the zones orregions a and with the longitudinal rods Within said zones designed toact as resilient cushioning or anchoring means for the slabs.

According to a further feature of improvement, especially whereindividual mats or reinforcing structures are provided for each gap 5,FIG. 2, the ends of the longitudinal rods may be bent to form feet forthe mounting or positioning of the mats or the like structures upon abase or road bed 21, as shown in FIGS. 11 and 12. If desirable, thecross-rods connecting the feet or bent portions 20 may be omitted.

In order to further decrease the cross-section of the slabs 1 in theregion of the gaps 5 to be formed, or to enhance the probability oftearing or rupturing of the concrete in forming the false gaps, theinserts 22 in FIGS. 11 and 12, corresponding to the sleeves 11 of FIG.5, are shown itted with an edgewise plate or strip 23 disposed in linewith the groove 3 and insert 4. Strip 23, consisting advantageously ofsynthetic material, is traversed by the longitudinal rods 7 with theinserts or sleeves 22 overlying said rods and taking the place of thebituminous or the like coatings of FIGS. 1 and 2 described hereinbefore.The effect of the strip 23 in further decreasing or weakening thecross-section of the slabs at the point where the gaps S are to beformed, is an added assurance of the formation of the gaps during theinitial use under actual load or traic conditions.

In applying the coatings 9 to or mounting of the sleeves 10, 11, 22 uponthe rods 7, care should be taken that the coatings or sleeves adhereclosely to the rod surface without the danger of being impaired 4ordistorted during the mounting and concrete pouring operations. The useof a synthetic strip. 23, FIG. 12, is of special importance or advantagewhere the upper groove 3i, instead of being cut into the hardened orcured concrete, is formed by the insertion of a movable bar or slatduring the concrete pouring operation or forming of the slabs.

In the foregoing the invention has been described in reference to a fewspecific illustrative devices. It will be evident, however, thatvariations and modifications, as well as the substitution of equivalentparts or elements for those shown for illustration, may be made withoutdeparting from the broader scope and spirit of the invention as setforth in the appended claims. The specification and drawings areaccordingly to be regarded in an illustrative rather than in arestrictive sense.

We claim:

1. A reinforced concrete roadway slab comprising in combination:

(1) a reinforcing mat structure embedded in said slab being composed of(a) a plurality of spaced longitudinal rods extending in the lengthwisedirection of slab, and

(b) a plurality of spaced transverse rods intersecting and being affixedto said longitudinal rods,

(c) said transverse rods being subdivided into groups with the rods ofeach group having a predetermined rod Spacing distance and with each twoadjacent groups being spaced from one another by an intermediate regionof the slab free from transverse rods and having a dimension in thelengthwise direction of the slab substantially in excess of said rodspacing distance,

(2) said slab being provided, midway within said region, with atransverse groove in at least the upper surface of the slab dening afracture line through said slab coincident with said groove, and

(3) means to provide for slidable engagement between the slab and atleast a fraction of the longitudinal rod sections coincident with saidintermediate slab region, whereby said longitudinal rod sections act asdowels for the concrete bodies of said slab on either side of said line.

2. In a concrete roadway slab as claimed in claim 1, said last meansconsisting of an adhesion-resistant coating upon at least one of theportions of the longitudinal rod sections located on either side of saidline.

3. In a concrete roadway slab as claimed in claim 1, said last meansconsisting of a bituminous coating upon at least one of the portions ofthe longitudinal rod sections located on either side of said line.

4. In a concrete roadway slab as claimed in claim 1, said last meansconsisting of tubular elements embedded in said slab and closelyenveloping at least one of the portions of the longitudinal rod sectionson either side of said line.

5. In a concrete roadway slab as claimed in claim 1, said last meansconsisting of tubular elements embedded in said slab symmetrically tosaid groove and closely enveloping said longitudinal rod sections, and aplatelike element embedded in said slab and extending normally to saidtubular elements in line with said groove.

6. In a concrete roadway slab as claimed in claim 1, including anadditional groove disposed in the undersurface of said slab in line withsaid rst groove.

References Cited UNITED STATES PATENTS 1,996,153 4/1935 Heltzel 94-392,015,340 9/ 1935 Fischer 94-8 2,060,326 11/1936 Lampert 94-17 2,080,1245/1937 Friberg 94-18 X 2,116,697 5/1938 Geyer 94-18 2,309,538 1/1943Robertson 94--18 2,806,414 9/1957 Woodman 94-17 3,022,713 2/ 1962Friberg 94--18 X 3,045,566 7/ 1962 Houck 94-93 3,156,169 11/ 1964Finsterwalder 94-8 2,106,095 1/ 1938 Heltzel 94-8 OTHER REFERENCESEngineering News Record: May 1957, p. 94.

JACOB L. NACKENOFF, Primary Examiner.

U.S. Cl. X.R. 94-18

